250 MANUAL OF THK MOLLUSCA. 
ScALARIA, Lam. Wentle-trap. 
Etymology, scalaris, like a ladder. 
Type, 8. pretiosa, Pl. [X., Fig. 9. (= T. scalaris, L.) 
Shell mostly pure white and lustrous; turreted; many- 
whorled; whorls round, sometimes separate, ornamented with 
numerous transyerse ribs; aperture round; peristome con- 
tinuous; operculum horny, few-whorled. 
Animal with a retractile proboscis-like mouth; tentacles 
close together, long and pointed, with the eyes near their outer 
bases ; mantle-margin simple, with a rudimentary siphonal 
fold; foot obtusely triangular, with a fold (mentum) in front. 
Lingual dentition nearly as in bulla; teeth 0; uncini nume- 
rous, simple; sexes distinct; predacious? Range from low 
water to 80 fathoms. The animal exudes a purple fluid when 
molested. 
Distribution, 104 species. Mostly tropical. Greenland, 
Norway, Britain, Mediterranean, West Indies, China, Australia, 
Pacific, West America. 
Fossil, nearly 100 species. Coral-rag—. Britain, North 
America, Chili, India. 
FAMILY VI.—LiTTORINIDA. 
Shell spiral, turbinated or depressed, never pearly; aperture 
rounded; peristome entire; operculum horny, pauci-spiral. 
Animal with a muzzle-shaped head, and eyes sessile at the 
outer bases of the tentacles ; tongue long, armed with a median 
series of broad, hooked. teeth, and 3 oblong, hooked uncini. 
Branchial plume single. Foot with a linear duplication in 
front, and a groove along the sole. Mantle with a rudimentary 
siphonal canal; operculum lobe appendaged. 
The species inhabit the sea, or brackish water, and are mostly 
littoral, feeding on algee. 
LitTToRINA, Férussac. Periwinkle. 
Litymology, littoralis, belonging to the sea-shore. 
Type, L. littorea, Pl. [X., Fig. 10. 
Shell turbinated, thick, pointed, few-whorled ; 
aperture rounded, outer lip acute, columella rather 
flattened, imperforate, operculum pauci-spiral, Fig. 
103. Lingual teeth hooked and trilobed; uncini 
Fig.103. hooked and dentated (Fig. 104). 
Distribution, 131 species. The periwinkles are found on the 
sea-shore in all parts of the world. In the Baltic they live 
